Instrument Removal System

ABSTRACT

An instrument removal system for removing detector cables from a nuclear reactor includes a removal cart and a disposal cask. in an exemplary embodiment, the removal cart includes a base including a plurality of wheels coupled thereto, a motor mounted on the base, and a drive shaft operatively coupled to the motor. A disposal spool is removably mounted on the drive shaft, and the disposal spool includes a notch sized to receive the detector cable. A housing is mounted on the base, with the housing enclosing the disposal spool. Also, an entrance port is located in the housing to permit the detector cable to enter the housing.

BACKGROUND OF THE INVENTION

This invention relates generally to nuclear reactors, and moreparticularly, to an instrument removal system to remove detector cablesfrom their housing.

A reactor pressure vessel (RPV) of a boiling water reactor (BWR)typically has a generally cylindrical shape and is closed at both ends,e.g., by a bottom head and a removable top head. A core assembly iscontained within the RPV and includes the core support plate, fuelassemblies, control rod blades and a top guide. A core shroud typicallysurrounds the core assembly and is supported by a shroud supportstructure. Particularly, the shroud has a generally cylindrical shapeand surrounds both the core plate and the top guide. There is a space orannulus located between the cylindrical reactor pressure vessel and thecylindrically shaped shroud.

A plurality of detectors are utilized to monitor the reactor.Periodically detectors need to be removed for replacement. The detectorsare typically positioned in a housing and are attached to cables fortransmitting data. A known method of removing detectors includes the useof a bottom entry disposal system which utilizes a pinch wheel system topull the detector cables from the housing. The detector cables are fedinto a cutter for cutting into small two inch pieces for disposal. Thedetector cable pieces are fed into a disposal cask for transport andremoval from the reactor. However, this method has some shortcomings,for example, pinch wheels can slip causing jammed detector cables and/ormissed cuts. Also, cutters can jam and generate loose, irradiated chips.Further, disposal casks can fill unevenly which can make cask lidsdifficult to close.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, an instrument removal system for removing detectorcables from a nuclear reactor is provided. The instrument removal systemincludes a removal cart and a disposal cask. The removal cart includes abase including a plurality of wheels coupled thereto, a motor mounted onthe base, and a drive shaft operatively coupled to the motor. A disposalspool is removably mounted on the drive shaft, and the disposal spoolincludes a notch sized to receive the detector cable. A housing ismounted on the base, with the housing enclosing the disposal spool.Also, an entrance port is located in the housing to permit the detectorcable to enter the housing.

In another aspect, a method of removing detectors from a nuclear reactorusing an instrument removal system is provided. the instrument removalsystem includes a removal cart and a disposal cask. The removal cartincludes a base, a plurality of wheels coupled to the base, a motormounted on the base, a drive shaft operatively coupled to the motor, adisposal spool removably mounted on the drive shaft, a notch in thedisposal spool sized to receive the detector cable, a housing mounted onthe base that encloses the disposal spool, an entrance port in thehousing sized to permit the detector cable to enter the housing. Thereactor includes a pressure vessel, an under vessel platform, and aplurality of transfer rails. The method includes positioning the removalcart under the reactor pressure vessel, attaching the detector cable tothe disposal spool, winding the detector cable onto the disposal spool,transferring the disposal spool to the disposal cask, and moving thedisposal cask from under the reactor pressure vessel.

In another aspect, a nuclear reactor is provided. The nuclear reactorincludes a reactor pressure vessel, an under vessel platform positionedbelow the reactor pressure vessel, a plurality of transfer railspositioned below the reactor pressure vessel, at least one detectorcable coupled to the reactor pressure vessel, and an instrument removalsystem operationally positioned on the transfer rails below the reactorpressure vessel. The instrument removal system includes a removal cartand a disposal cask. The removal cart includes a base including aplurality of wheels coupled thereto, a motor mounted on the base, and adrive shaft operatively coupled to the motor. A disposal spool isremovably mounted on the drive shaft, and the disposal spool includes anotch sized to receive the detector cable. A housing is mounted on thebase, with the housing enclosing the disposal spool. Also, an entranceport is located in the housing to permit the detector cable to enter thehousing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional schematic illustration, with parts cut away, of aboiling water nuclear reactor.

FIG. 2 is a sectional schematic illustration of the under pressurevessel area of the nuclear reactor shown in FIG. 1

FIG. 3 is a side schematic illustration of an instrument removal systemin accordance with an embodiment of the present invention.

FIG. 4 is a side schematic illustration of the instrument removal systemshown in FIG. 3 with a detector cable partially coiled around a disposalspool.

FIG. 5 is a side schematic illustration of the instrument removal systemshown in FIG. 3 with the disposal spool being transferred to a disposalcask.

FIG. 5 is a side schematic illustration of the instrument removal systemshown in FIG. 3 with the disposal spool transferred to the disposalcask.

DETAILED DESCRIPTION OF THE INVENTION

An instrument removal system and method of removing detectors from anuclear reactor is described in detail below. The system includes aremoval cart that includes a disposal spool operatively coupled to amotor. A detector cable is coiled around the spool by rotating the spoolwith the motor, and then the disposal spool is transferred to a disposalcask for removal from the reactor. The removal system does not have acable cutting process which eliminates loose chips and/or jammed cuttersthat need be cleared by personnel. The removal system utilizes existingunder vessel equipment, for example, under vessel platform and rails,has low complexity with minimal operator interface resulting in lowerpersonnel exposure to radiation.

Referring to the drawings, FIG. 1 is a sectional view, with parts cutaway, of a boiling water nuclear reactor pressure vessel (RPV) 10. RPV10 has a generally cylindrical shape and is closed at one end by abottom head 12 and at its other end by a removable top head 14. Aside-wall 16 extends from bottom head 12 to top head 14. Side-wall 16includes a top flange 18. Top head 14 is attached to top flange 18. Acylindrically shaped core shroud 20 surrounds a reactor core 22. Shroud20 is supported at one end by a shroud support 24 and includes aremovable shroud head 26 at the other end. An annulus 28 is formedbetween shroud 20 and side-wall 16. A pump deck 30, which has a ringshape, extends between shroud support 24 and RPV side-wall 16. Pump deck30 includes a plurality of circular openings 32, with each openinghousing a jet pump 34. Jet pumps 34 are circumferentially distributedaround core shroud 20. An inlet riser pipe 36 is coupled to two jetpumps 34 by a transition assembly 38. Each jet pump 34 includes an inletmixer 40, a diffuser 42, and a tailpipe assembly 43. Inlet riser 36 andtwo connected jet pumps 34 form a jet pump assembly 44.

Thermal power is generated within core 22, which includes fuelassemblies 46 of fissionable material. Water circulated up through core22 is at least partially converted to steam. Steam separators 48separates steam from water, which is recirculated. Residual water isremoved from the steam by steam dryers 50. The steam exits RPV 10through a steam outlet 52 near vessel top head 14.

The amount of thermal power generated in core 22 is regulated byinserting and withdrawing control rods 54 of neutron absorbing material,such as for example, boron carbide. To the extent that control rod 54 isinserted into core 22 between fuel assemblies 46, it absorbs neutronsthat would otherwise be available to promote the chain reaction whichgenerates thermal power in core 22. Control rod guide tubes 56 maintainthe vertical motion of control rods 54 during insertion and withdrawal.Control rod drives 58 effect the insertion and withdrawal of controlrods 54. Control rod drives 58 extend through bottom head 12.

Fuel assemblies 46 are aligned by a core plate 60 located at the base ofcore 22. A top guide 62 aligns fuel bundles 46 as they are lowered intocore 22. Core plate 60 and top guide 62 are supported by core shroud 20.Pressure vessel 10 is mounted on a reinforced concrete pedestal 66

FIG. 2 is a sectional schematic illustration of an under pressure vesselarea 70 of nuclear reactor pressure vessel 10 enclosed by pedestal 66.Under pressure vessel area 70 includes a work platform 72 and transferrails 74 that can be used for moving work equipment into under vesselarea 70.

Referring to FIGS. 3-6, an instrument removal system 80 for removingdetector cables 82 from nuclear reactor pressure vessel 10 includes, inan exemplary embodiment, a removal cart 84 and a disposal cask 86.Removal cart 84 includes a base 88 with a plurality of wheels 90operatively coupled to base 88. Wheels 90 permit removal cart to movealong transfer rails 74. A motor 92 mounted on base 88, and a driveshaft 94 is operatively coupled to motor 92. Motor 92 can be anysuitable motor, for example, an electric motor, an hydraulic drivenmotor, and an air driven motor. A disposal spool 96 is removably mountedon drive shaft 94. Disposal spool 96 includes a notch 98 sized toreceive an end of detector cable 82. Disposal spool 96 also includes aspiral groove 100 to facilitate coiling detector cable 82 arounddisposal spool 96.

A bearing block 102 is mounted on base 88 with drive shaft 94 extendingthrough bearing block 102. At least one air piston 104 (two shown) ismounted in bearing block 102. FIGS. 3 and 4 show air pistons 104 in afirst, non-extended position, and FIGS. 5 and 6 show air pistons 104 inan activated extended position. A housing 106 is mounted on base 88 withdisposal spool 96, drive shaft 94, bearing block 102, and air pistons104 positioned inside housing 106. An entrance port 108 is located inhousing 106 to permit detector cable 82 to enter housing 106. In theexemplary embodiment entrance port 108 is formed from a transparent tubeto permit remote visual monitoring during detector removal. A door 110is located in one side of housing 106 that permits removal of disposalspool 96 from housing 106 when door 110 is in an open position (shown inFIGS. 5 and 6).

Disposal cask 86 includes a main body 114 having a receiving cavity 116therein. Cavity 116 is sized to receive at least one disposal spool 96.An access door 118 permits access to cavity 116. When door 118 is in anopen position, a disposal spool can be transferred into cavity 116. Whendoor 118 is in a closed position, cavity 116 is sealed. A plurality ofwheels 120 are operatively coupled to main body 114 to enable disposalcask 86 to move along rails 74 in under vessel area 70.

In operation, instrument removal system 80 is first positioned in underpressure vessel area 70. Particularly, removal cart 84 and disposal cask86 are wheeled into under vessel area 70, and then an end of a detectorcable 82 is inserted into notch 98 of disposal spool 96 in removal cart84. Air motor 92 is activated to coil detector cable 82 onto disposalspool 96. After the entire length of detector cable 82 is coiled ontodisposal spool 96, disposal spool 96 is transferred to disposal cask 86by activating air pistons 104 to push disposal spool 96 off drive shaft94, out door 106 and into disposal cask 86 through access door 118.Disposal cask 86 is then removed from under vessel area 70.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

1.-6. (canceled)
 7. A method of removing detectors from a nuclearreactor using an instrument removal system comprising a removal cart anda disposal cask, the removal cart comprising a base, a plurality ofwheels coupled to the base, a motor mounted on the base, a drive shaftoperatively coupled to the motor, a disposal spool removably mounted onthe drive shaft, a notch in the disposal spool sized to receive thedetector cable, a housing mounted on the base that encloses the disposalspool, an entrance port in the housing sized to permit the detectorcable to enter the housing, the reactor comprising a pressure vessel, anunder vessel platform, and a plurality of transfer rails, said methodcomprising: positioning the removal cart under the reactor pressurevessel; attaching the detector cable to the disposal spool; winding thedetector cable onto the disposal spool; transferring the disposal spoolto the disposal cask; and moving the disposal cask from under thereactor pressure vessel.
 8. A method in accordance with claim 7 whereinattaching the detector cable comprises inserting the detector cable intothe notch in the disposal spool.
 9. A method in accordance with claim 7wherein winding the detector cable onto the disposal spool comprisesactivating the motor to turn the drive shaft and the disposal spool. 10.A method in accordance with claim 7 wherein the disposal cask comprisesa main body having a cavity therein sized to receive at least onedisposal spool, an access door in the main body that permits access tothe cavity when the access door is in an open position, and a pluralityof wheels operatively coupled to the main body, and transferring thedisposal spool to the disposal cask comprises activating the air pistonsto extend and push the disposal spool off the drive shaft and out thehousing door into the disposal cask.
 11. A method in accordance withclaim 10 wherein transferring the disposal spool to the disposal caskfurther comprises activating the air pistons to extend and push thedisposal spool off the drive shaft and out the housing door into thedisposal cask through the access door.
 12. A method in accordance withclaim 10 wherein moving the disposal cask from under the reactorpressure vessel comprises rolling the disposal cask along the transferrails on the disposal cask wheels. 13.-18. (canceled)
 19. A method ofremoving detector cables from a nuclear reactor, the reactor comprisinga pressure vessel, an under vessel platform, and a plurality of transferrails, said method comprising: providing an instrument removal system,the instrument removal system comprising: a removal cart and a disposalcask, the removal cart comprising a base, a plurality of wheels coupledto the base, a motor mounted on the base, a drive shaft operativelycoupled to the motor, a disposal spool removably mounted on the driveshaft, a notch in the disposal spool sized to receive the detectorcable, a housing mounted on the base that encloses the disposal spool,an entrance port in the housing sized to permit the detector cable toenter the housing; positioning the removal cart under the reactorpressure vessel with the removal cart wheels riding on the transferrails; attaching the detector cable to the disposal spool; winding thedetector cable onto the disposal spool; transferring the disposal spoolto the disposal cask; and moving the disposal cask from under thereactor pressure vessel.
 20. A method in accordance with claim 19wherein attaching the detector cable comprises inserting the detectorcable into the notch in the disposal spool.
 21. A method in accordancewith claim 19 wherein winding the detector cable onto the disposal spoolcomprises activating the motor to turn the drive shaft and the disposalspool.
 22. A method in accordance with claim 19 wherein the disposalcask comprises a main body having a cavity therein sized to receive atleast one disposal spool, an access door in the main body that permitsaccess to the cavity when the access door is in an open position, and aplurality of wheels operatively coupled to the main body, andtransferring the disposal spool to the disposal cask comprisesactivating the air pistons to extend and push the disposal spool off thedrive shaft and out the housing door into the disposal cask.
 23. Amethod in accordance with claim 22 wherein transferring the disposalspool to the disposal cask further comprises activating the air pistonsto extend and push the disposal spool off the drive shaft and out thehousing door into the disposal cask through the access door.
 24. Amethod in accordance with claim 22 wherein moving the disposal cask fromunder the reactor pressure vessel comprises rolling the disposal caskalong the transfer rails on the disposal cask wheels.
 25. A method ofremoving detector cables from a nuclear reactor, the reactor comprisinga pressure vessel, an under vessel platform, and a plurality of transferrails, said method comprising: providing an instrument removal system,the instrument removal system comprising: a removal cart and a disposalcask, the removal cart comprising: a base, a plurality of wheels coupledto the base, a motor mounted on the base, a drive shaft operativelycoupled to the motor, a disposal spool removably mounted on the driveshaft, a notch in the disposal spool sized to receive the detectorcable, a housing mounted on the base that encloses the disposal spool,an entrance port in the housing sized to permit the detector cable toenter the housing, the disposal cask comprising: a main body having acavity therein sized to receive at least one disposal spool, an accessdoor in the main body that permits access to the cavity when the accessdoor is in an open position, and a plurality of wheels operativelycoupled to the main body; positioning the removal cart under the reactorpressure vessel with the removal cart wheels riding on the transferrails; attaching the detector cable to the disposal spool; winding thedetector cable onto the disposal spool; transferring the disposal spoolto the disposal cask; and moving the disposal cask from under thereactor pressure vessel.
 26. A method in accordance with claim 25wherein attaching the detector cable comprises inserting the detectorcable into the notch in the disposal spool.
 27. A method in accordancewith claim 25 wherein winding the detector cable onto the disposal spoolcomprises activating the motor to turn the drive shaft and the disposalspool.
 28. A method in accordance with claim 25 wherein transferring thedisposal spool to the disposal cask comprises activating the air pistonsto extend and push the disposal spool off the drive shaft and out thehousing door into the disposal cask.
 29. A method in accordance withclaim 28 wherein transferring the disposal spool to the disposal caskfurther comprises activating the air pistons to extend and push thedisposal spool off the drive shaft and out the housing door into thedisposal cask through the access door.
 30. A method in accordance withclaim 25 wherein moving the disposal cask from under the reactorpressure vessel comprises rolling the disposal cask along the transferrails on the disposal cask wheels.